Electrocardiograph device having additional lead function and method for obtaining additional-lead electrocardiogram

ABSTRACT

There are provided an electrocardiograph with an extended lead function and an extended lead ECG deriving method capable of easily deriving an ECG signal of an extended lead ECG by an arithmetic operation, based on ECG signals of a standard 12-lead ECG measured by a potential detector  10 . An ECG memory  12  stores the ECG signals measured as the standard 12-lead ECG by the potential detector  10 . An extended lead ECG calculator  16  calculates extended lead ECGs V 7 -V 9  from the ECG signals stored in the ECG memory  12 , using coefficients α representing a relationship among leads. The extended lead ECGs V 7 -V 9  calculated are displayed through an extended lead ECG waveform outputting device  18  on a display monitor  20.

TECHNICAL FIELD

The present invention relates to an electrocardiograph with an extendedlead function and an extended lead electrocardiogram (ECG) derivingmethod capable of easily and correctly obtaining through an arithmeticoperation, an extended lead ECG effective to diagnoses of an ischemicheart disease, an acute cardiac infarction, etc. in the cardiac muscleregions difficult to diagnose even with the standard 12-lead ECG.

BACKGROUND ART

For measuring an ECG of a patient, ten electrodes connected to anelectrocardiograph are used as mounted at six locations for measurementof chest leads and at four locations for measurement of limb leads. Thenthe electrocardiograph calculates and outputs the six limb leadwaveforms (I, II, III, aVR, aVL, and aVF) of the standard 12 leads andthe six chest lead waveforms (V1, V2, V3, V4, V5, and V6) of thestandard 12 leads, based on heart potentials detected from these tenelectrodes.

In general, the relationship based on that the standard 12-lead ECG isobtained is given as described in [Table 1] below. TABLE 1 Lead I: vL −vR Lead II: vF − vR Lead III: vF − vL Lead aVR: vR − (vL + vF)/2 LeadaVL: vL − (vR + vF)/2 Lead aVF: vF − (vL + vR)/2 Lead V1: v1 − (vR +vL + vF)/3 Lead V2: v2 − (vR + vL + vF)/3 Lead V3: v3 − (vR + vL + vF)/3Lead V4: v4 − (vR + vL + vF)/3 Lead V5: v5 − (vR + vL + vF)/3 Lead V6:v6 − (vR + vL + vF)/3

In the above relationship, each v represents a potential detected at theelectrode-mounted position.

The diagnosis of a patient's heart disease with a number of electrodesas described above can be performed in rest state in a bed of thepatient as long as it is done within a fully-equipped hospital or thelike.

However, for example, in cases of home and emergency medical cares, itis often the case that there is no extra room for use of many electrodesand attachment of each electrode at the appropriate position on the bodysurface of the living body in view of the patient's condition.Furthermore, it is sometimes difficult to transmit signals of multiplechannels for acquisition of many lead waveforms. In such cases, only onechannel (one lead) is commonly used to transmit the ECG signals, and thediagnosis of the heart disease is made by using at most two to fourelectrodes to measure some lead waveforms out of the standard 12-leadwaveforms.

Under such circumstances, the inventor has developed a constructionmethod of a standard 12-lead ECG and an ECG inspection apparatus forreconstructing the standard 12-lead ECG permitting appropriate diagnosesand treatment of various heart diseases, based on a subset of a leadsystem consisting of a minimum number of leads for acquisition of theconventionally known standard 12-lead ECG, and filed a patentapplication (cf. Patent Document 1).

Specifically, the construction method of the standard 12-lead ECGdescribed in the above Patent Document 1 uses as the subset of the leadsystem consisting of the minimum number of channels, Leads I and II ofthe limb leads, and two leads of the chest leads, Lead V1 and, Lead V5or Lead V6, for acquisition of the standard 12-lead ECG. Using theseleads, Lead III and Leads aV (Lead aVR, Lead aVL, and Lead aVF) can bedetermined by an arithmetic operation based on the characteristicrelationship among the leads presented in Table 1. The remaining leadsof the chest leads, Lead V2, Lead V3, Lead V4, and, Lead V6 or Lead V5,can be determined by an arithmetic operation from the relationship amongpotentials, lead vectors, and a heart vector.

Since the standard 12-lead ECG obtained in this manner uses the subsetof the lead system of the conventional standard 12-lead ECG, eachelectrode can be mounted as readily and accurately positioned at eachpredetermined location and this work does not require much skill. Inaddition, the standard 12-lead ECG can be reconstructed with highprecision, so that the diagnoses and treatment can be appropriatelyperformed for the various heart diseases.

However, not only in the case where the standard 12-lead ECG is obtainedfrom the six limb leads and six chest leads with the ten electrodes asbefore, but also in the case where the highly accurate standard 12-leadECG is obtained by the method described in Patent Document 1 as above,it is relatively easy to confirm and diagnose an anomaly in the ECGwaveforms, for example, if an occlusion of the coronary artery feedingblood to the heart muscle among the cardiac infarctions occurs in theanterior wall, the lateral wall, or the inferior wall of the heartmuscle. On the contrary, if an occlusion of the coronary artery occursat the posterior wall of the heart muscle, the electrode mountedlocations are far from the posterior wall and the sensitivity of the ECGwaveforms is thus too low to reflect the effect of the occlusion of thecoronary artery on the ECG waveforms. In addition, the sensitivity tothe right lateral wall of the heart muscle is also low because most ofthe electrode mounted positions of the standard 12-lead ECG are on theleft side of the body surface. For this reason, it is highly likely thatthe occlusion of the coronary artery at the posterior wall, the rightlateral wall, or the right inferior wall is overlooked in the diagnosis.

[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-34943

It was thus conventionally common practice to obtain an extended leadECG using Leads V7, V8, and V9 measured at electrode mounted locationson extensions of the chest leads and/or using Leads V3R, V4R, V5R, andV6R at electrode locations symmetric with the electrode locations of thechest leads, in order to make correct diagnoses of the aforementionedposterior myocardial infarction, pulmonary heart, pulmonary embolus,right ventricular infarction, right ventricular hypertrophy,dextrocardia, other stress-related right ventricular diseases, and soon. However, the electrode mounted positions for acquisition of theextended lead ECG of Leads V7, V8, and V9 are on the patient's back orthe like. The patient needs to lie back in order to be kept at rest,whereas the patient is forced into an unnatural posture in order tomount the electrodes on the patient's back or the like. In addition,there also arises a problem that the electrode mounting operation iscomplicated. Moreover, the ordinary standard 12-lead electrocardiographsare unable to measure the extended lead ECG of Leads V7, V8, and V9 andLeads V3R, V4R, V5R, and V6R, and there arises a need for a specialelectrocardiograph with an extended lead ECG measuring function havingthe electrodes for measurement of the extended leads.

DISCLOSURE OF THE INVENTION

An object of the present invention is to solve the problems in theconventional technology as described above and to easily obtain anextended lead, without need for mounting an additional electrode otherthan the electrodes used for the 12 leads. Another object of the presentinvention is to easily obtain an extended lead, without need formounting an electrode for the extended lead, from some of the leads ofthe 12-lead ECG.

The above objects of the present invention are achieved by providing anelectrocardiograph with an extended lead function comprising a potentialdetector for measuring lead potentials of a 12-lead ECG or at least partof them; and extended lead potential calculating means for calculatingan extended lead potential, based on the lead potentials of the 12-leadECG or the part of the lead potentials measured by the potentialdetector.

In a preferred embodiment of the present invention, the extended leadpotential calculating means uses a relationship among the measured leadpotentials, a heart vector, and lead vectors to determine the heartvector on the basis of the lead potentials measured by the potentialdetector, and calculates the extended lead potential by use of the heartvector thus determined.

The extended lead potential calculating means may calculate the extendedlead potential on the basis of the lead potentials measured by thepotential detector, using transfer coefficients α representing arelationship among the leads.

The above objects of the present invention can also be achieved byperforming an extended lead ECG deriving method comprising a first stepof measuring at least part of lead potentials of a 12-lead ECG, and asecond step of calculating an extended lead potential, based on themeasured lead potentials out of the lead potentials of the 12-lead ECG.

In this extended lead ECG deriving method, preferably, the second stepalso comprises using a relationship among the lead potentials, a heartvector, and lead vectors to determine the heart vector on the basis ofthe measured lead potentials, and calculating the extended leadpotential by use of the heart vector thus determined.

Alternatively, the second step may comprise calculating the extendedlead potential on the basis of the measured lead potentials, usingtransfer coefficients α representing a relationship among the leads.

A method of deriving an extended lead ECG according to the presentinvention comprises performing an arithmetic operation to calculate alead potential at an extended lead location except for a standard12-lead ECG, based on ECG signals measured as standard lead potentialsof the standard 12-lead ECG by a potential detector consisting of ten orless electrodes.

Another method of deriving an extended lead ECG according to the presentinvention comprises, based on ECG signals measured as standard leadpotentials of a standard 12-lead ECG by a potential detector consistingof ten or less electrodes, determining a heart vector [H] on the basisof the measured ECG signals as the standard lead potentials of thestandard 12-lead ECG from a relationship among the potentials [V], leadvectors [L], and the heart vector [H], and performing an arithmeticoperation to calculate an extended lead potential of an extended leadECG, using the heart vector [H] thus determined.

Still another method of deriving an extended lead ECG according to thepresent invention comprises storing ECG signals measured as standardlead potentials of a standard 12-lead ECG by a potential detectorconsisting of ten or less electrodes, performing an arithmetic operationto set transfer coefficients α for calculation of an extended leadpotential on the basis of the standard lead potentials of the standard12-lead ECG and extended lead potentials of the extended lead ECGmeasured in advance, and performing an arithmetic operation to calculatethe extended lead potential of the extended lead ECG from the ECGsignals measured as the standard lead potentials of the standard 12-leadECG, using the transfer coefficients α set by the arithmetic operation.

Still another method of deriving an extended lead ECG according to thepresent invention comprises storing ECG signals measured as a standard12-lead ECG by a potential detector, performing an arithmetic operationto set parameters for calculation of an extended lead ECG on the basisof lead potentials of the standard 12-lead ECG and lead potentials ofthe extended lead ECG measured in advance, and performing an arithmeticoperation to calculate a lead potential of the extended lead ECG fromthe ECG signals measured as the standard 12-lead ECG, using theparameters set by the arithmetic operation.

Another electrocardiograph with an extended lead function according tothe present invention comprises electrodes to be mounted on a bodysurface of a living body in order to obtain lead waveforms of a standard12-ECG; a potential detector for measuring ECG signals of the standard12-lead ECG from the respective electrodes; an ECG signal memory forstoring each of the ECG signals of the standard 12-lead ECG measured bythe potential detector; standard 12-lead ECG waveform means forperforming waveform processing of the standard 12-lead ECG with input ofthe ECG signals obtained via the ECG signal memory; extended lead ECGsignal calculating means for calculating an ECG signal of an extendedlead ECG on the basis of calculation parameters α set in advance by anarithmetic operation with input of the ECG signals obtained via the ECGsignal memory; extended lead ECG waveform outputting means forperforming waveform processing of the extended lead ECG with input ofthe ECG signal calculated by the extended lead ECG signal calculatingmeans; and a display monitor for simultaneously displaying on a screen,ECG waveform outputs from the standard 12-lead ECG waveform outputtingmeans and from the extended lead ECG waveform outputting means.

The foregoing extended lead ECG preferably comprises some or all ofLeads V7-V9, and Leads V_(3R), V_(4R), V_(5R), and V_(6R).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram showing the first embodiment ofthe electrocardiograph according to the present invention.

FIG. 2 is a flowchart showing the operation of the electrocardiographshown in FIG. 1.

FIG. 3 is a waveform diagram for comparison between an extended lead ECGof Lead V7 derived in the first embodiment and an extended lead ECGbased on measured values.

FIG. 4 is a waveform diagram for comparison between an extended lead ECGof Lead V8 derived in the first embodiment and an extended lead ECGbased on measured values.

FIG. 5 is a waveform diagram for comparison between an extended lead ECGof Lead V9 derived in the first embodiment and an extended lead ECGbased on measured values.

FIG. 6 is a system configuration diagram showing the second embodimentof the electrocardiograph according to the present invention.

FIG. 7 is a flowchart showing the operation of the electrocardiographshown in FIG. 6.

FIG. 8 is a system configuration diagram showing the third embodiment ofthe electrocardiograph according to the present invention.

FIG. 9 is a flowchart showing the operation of the electrocardiographshown in FIG. 8.

FIG. 10 is a system configuration diagram showing the fourth embodimentof the electrocardiograph according to the present invention.

FIG. 11 is a flowchart showing the operation of the electrocardiographshown in FIG. 9.

In FIG. 12, (a) shows measured waveforms of ECG signals (I, II, V2, andV4) of the standard 12-lead ECG, (b) calculated waveforms and measuredwaveforms of Leads V3R, V4R, and V5R of the extended lead ECG, and (c)calculated waveforms and measured waveforms of Leads V7, V8, and V9 ofthe extended lead ECG.

In FIG. 13, (a) shows measured waveforms of ECG signals (I, II, V2, andV5) of the standard 12-lead ECG, (b) calculated waveforms and measuredwaveforms of Leads V3R, V4R, and V5R of the extended lead ECG, and (c)calculated waveforms and measured waveforms of Leads V7, V8, and V9 ofthe extended lead ECG.

In FIG. 14, (a) shows measured waveforms of ECG signals (I, II, V2, andV6) of the standard 12-lead ECG, (b) calculated waveforms and measuredwaveforms of Leads V3R, V4R, and V5R of the extended lead ECG, and (c)calculated waveforms and measured waveforms of Leads V7, V8, and V9 ofthe extended lead ECG.

In FIG. 15, (a) shows measured waveforms of ECG signals (I, II, V1, andV5) of the standard 12-lead ECG, (b) calculated waveforms and measuredwaveforms of Leads V3R, V4R, and V5R of the extended lead ECG, and (c)calculated waveforms and measured waveforms of Leads V7, V8, and V9 ofthe extended lead ECG.

In FIG. 16, (a) shows measured waveforms of ECG signals (I, II, V1, andV6) of the standard 12-lead ECG, (b) calculated waveforms and measuredwaveforms of Leads V3R, V4R, and V5R of the extended lead ECG, and (c)calculated waveforms and measured waveforms of Leads V7, V8, and V9 ofthe extended lead ECG.

In FIG. 17, (a) shows measured waveforms of ECG signals (I, II, V3, andV4) of the standard 12-lead ECG, (b) calculated waveforms and measuredwaveforms of Leads V3R, V4R, and V5R of the extended lead ECG, and (c)calculated waveforms and measured waveforms of Leads V7, V8, and V9 ofthe extended lead ECG.

In FIG. 18, (a) shows measured waveforms of ECG signals (I, II, V3, andV5) of the standard 12-lead ECG, (b) calculated waveforms and measuredwaveforms of Leads V3R, V4R, and V5R of the extended lead ECG, and (c)calculated waveforms and measured waveforms of Leads V7, V8, and V9 ofthe extended lead ECG.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will be describedbelow in detail with reference to the drawings.

First Embodiment

The first embodiment concerns a method and apparatus for making use ofECG signals measured at the electrode mounted locations of the standard12-lead ECG by a potential detector of a standard 12-leadelectrocardiograph, to perform an arithmetic operation to calculate, forexample, extended leads including Leads V7, V8, and V9 at electrodemounted locations on extensions of the chest leads and Leads V_(3R),V_(4R), and V_(5R).

Namely, the first embodiment is to calculate the extended leads V7, V8,V9 and V_(3R), V_(4R), V_(5R), for example, from the eight ECG signals(I, II, V1, V2, V3, V4, V5, and V6) obtained by the standard 12-leadelectrocardiograph, in order to calculate the heart potentials at theextended lead locations (ECG) from the ECG signals obtained by thepotential detector of the 12-lead electrocardiograph.

(Principle of Method of Deriving Extended Lead ECG Using Lead Vectors)

In the clinical ECG, according to the lead theory, the cardiac source atan arbitrary time can be expressed by a Fixed Single Dipole and apotential (V) at an arbitrary lead location can be determined by Eqs(1-1) to (1-3) below. $\begin{matrix}{V = {L \cdot H}} & \left( {1\text{-}1} \right) \\{H = \begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}} & \left( {1\text{-}2} \right) \\{L = \begin{pmatrix}{lx} \\{ly} \\{lz}\end{pmatrix}} & \left( {1\text{-}3} \right)\end{matrix}$

In the above equations, V represents a potential matrix, H the heartvector, and L a lead vector.

Therefore, the heart vector H varies depending upon the electricactivity of the heart and the inner product of the heart vector H andthe lead vector L provides a cardiac potential (ECG) V measured by theelectrocardiograph. Since each lead vector L is defined by valuesinherent to a specific person, the cardiac potential can be determinedby a spatial vector of electromotive force of the heart. Namely, acardiac potential of an arbitrary lead can be determined by threeparameters.

Accordingly, since the potential detector of the standard 12-leadelectrocardiograph measures the eight ECG signals, it is possible tocalculate an ECG potential at an arbitrary location on a body surface ofa living body by use of these ECG signals. For example, where theextended leads V7, V8, V9, V_(3R), V_(4R), and V_(5R) are calculatedfrom the ECG signals (I, II, V1, V2, V3, V4, V5, and V6) measured by thepotential detector of the standard 12-lead electrocardiograph, eachextended lead can be expressed by Eq (1-4) below. $\begin{matrix}{V_{i} = {\sum\limits_{j}{\alpha_{i,j}V_{j}}}} & \left( {1\text{-}4} \right)\end{matrix}$

In the above equation, i indicates a lead number of each extended lead(V7, V8, V9, V_(3R), V_(4R), or V_(5R)), and j a lead number of each ofthe standard 12 leads (I, II, V1, V2, V3, V4, V5, and V6). Furthermore,α stands for transfer coefficients representing the relationship amongthe leads.

The parameters α in the equation expressed by Eq (1-4) are constantstheoretically determined by the torso structure of each individual, butunknowns in Eq (1-4). The parameters α can be determined as a solutionof the least-squares computation by actually measuring Leads I, II, V1,V2, V3, V4, V5, and V6 of the standard 12 leads and Leads V7, V8, V9,V_(3R), V_(4R), and V_(5R) of the extended leads in advance andsubstituting them into Eq (1-5) below.A=(V ^(T) _(j) V _(j))⁻¹ V ^(T) _(j) V _(i)  (1-5)

In the above equation, A={α_(ij)}

V_(j)={V_(s,j)}

V_(i)={V_(i,s)}

T represents the transposition of a vector, and s a data sample.

Once the parameters α are determined in this manner, Leads V7, V8, andV9 and Leads V_(3R), V_(4R), V_(5R) of the extended leads can be readilydetermined immediately from the ECG signals to derive the standard12-lead ECG, based on Eq (1-4).

Accordingly, the ECG signals of the extended lead ECG except for thestandard 12-lead ECG can be easily derived by the arithmetic operation,from the ECG signals of the standard 12-lead ECG measured by thepotential detector.

(Configuration of Electrocardiograph with Function for Deriving ExtendedLead ECG)

FIG. 1 is a system configuration diagram of an electrocardiograph withan extended lead function for deriving the ECG signals of the extendedlead ECG from the ECG signals of the standard 12-lead ECG in the firstembodiment. In FIG. 1, specifically, reference numeral 10 denotes apotential detector for detecting the ECG signals of the standard 12-leadECG. This potential detector 10 functions as a bioamplifier and as anA/D converter for measuring the ECG signals (I, II, V1, V2, V3, V4, V5,and V6) from the electrodes (RA, LA, RL, LL, V1, V2, V3, V4, V5, and V6)mounted on a body surface of a living body for acquisition of the leadwaveforms of the standard 12-lead ECG.

Each of the ECG signals (I, II, V1, V2, V3, V4, V5, and V6) of thestandard 12 leads detected by the potential detector 10 is stored in anECG signal memory 12 and fed to a standard 12-lead ECG waveform outputdevice 14. The ECG signals (I, II, V1, V2, V3, V4, V5, and V6) stored inthe ECG signal memory 12 are also fed to an extended lead ECG calculator16. The extended lead ECG calculator 16 performs an arithmetic operationto calculate the ECG signals (V7, V8, and V9) of the extended lead ECG,based on the calculation parameters α set in advance in a memory 15described later, and outputs them to an extended lead ECG waveformoutput device 18.

The ECG waveform outputs from the standard 12-lead ECG waveform outputdevice 14 and from the extended lead ECG waveform output device 18 arethen fed each to a display monitor 20. Then the display monitor 20simultaneously displays the standard 12-lead ECG and the extended leadECG.

The calculation parameters α herein may be values of an average modelobtained from the population. Specifically, the ECG signals consistingof the lead potentials (I, II, V1, V2, V3, V4, V5, V6) of the standard12 leads and the lead potentials (V7, V8, V9, V_(3R), V_(4R), V_(5R)) ofthe extended leads are collected from the population of patients,healthy individuals, etc. by the potential detector 10, to construct adatabase in the extended lead ECG calculator 16. Then the extended leadECG calculator 16 calculates the calculation parameters α of the averagemodel from the data in the database and stores the values α in thememory 15. The calculation parameters α can be calculated based on theaforementioned Eq (1-5).

The system operation of the electrocardiograph with the extended leadfunction constructed as described above will be described below withreference to the flowchart shown in FIG. 2.

Specifically, in the electrocardiograph with the extended lead functionin the first embodiment, the potential detector 10 first measures theECG signals (I, II, V1, V2, V3, V4, V5, and V6) of the standard 12-leadECG of a patient (STEP-101). The ECG signals of the standard 12-lead ECGthus measured are stored into the ECG signal memory 12 (STEP-102). Thenthe calculation parameters α preliminarily set in the memory 15 are fedto the extended lead ECG calculator 16 (STEP-103). Thereafter, theextended lead ECG calculator 16 performs the arithmetic operation tocalculate the ECG signals (V7, V8, V9, V_(3R), V_(4R), and V_(5R)) ofthe extended lead ECG, based on the patient's ECG signals stored in theECG signal memory 12 and the calculation parameters α (STEP-104). Thisarithmetic operation to calculate the ECG signals (V7, V8, V9, V_(3R),V_(4R), and V_(5R)) of the extended lead ECG by the extended lead ECGcalculator 16 can be performed according to Eqs (1-6) to (1-11) below,based on the aforementioned Eq (1-4).Lead V7: V ₇=α_(7I) V _(I)+α_(7II) V _(II)+α_(7V1) V _(V1)+α_(7V2) V_(V2)+ . . . +α_(7V6) V _(V6)  (1-6)Lead V8: V ₈=α_(8I) V _(I)+α_(8II) V _(II)+α_(8V1) V _(V1)+α_(8V2) V_(V2)+ . . . +α_(8V6) V _(V6)  (1-7)Lead V9: V ₉=α_(9I) V _(I)+α_(9II) V _(II)+α_(9V1) V _(V1)+α_(9V2) V_(V2)+ . . . +α_(9V6) V _(V6)  (1-8)Lead V _(3R) : V _(3R)=α_(3RI) V _(I)+α_(3RII) V _(II)+α_(3RV1) V_(V1)+α_(3RV2) V _(V2)+ . . . +α_(3RV6) V _(V6)  (1-9)Lead V _(4R) : V _(4R)=α_(4RI) V _(I)+α_(4RII) V _(II)+α_(4RV1) V_(V1)+α_(4RV2) V _(V2)+ . . . +α_(4RV6) V _(V6)  (1-10)Lead V _(5R) : V _(5R)=α_(5RI) V _(I)+α_(5RII) V _(II)+α_(5RV1) V_(V1)+α_(5RV2) V _(V2)+ . . . +α_(5RV6) V _(V6)  (1-11)

The ECG signals (V7, V8, V9, V_(3R), V_(4R), and V_(5R)) of the extendedlead ECG calculated in this manner are then subjected to waveformprocessing by the extended lead ECG waveform output device 18 (STEP-105)and the ECG signals (I, II, V1, V2, V3, V4, V5, and V6) of the standard12-lead ECG stored in the ECG signal memory 12 are subjected to waveformprocessing by the standard 12-lead ECG waveform output device 14(STEP-106), and the results are fed each to the display monitor 20. Thedisplay monitor 20 simultaneously displays the standard 12-lead ECG andthe extended lead ECG thus fed, on a display screen (STEP-107).

A comparison was made between the extended lead ECG consisting of LeadsV7, V8, and V9 calculated from the ECG signals of the standard 12-leadECG on the basis of the first embodiment and the extended lead ECG basedon actually measured values of respective Leads V7, V8, and V9, and theresults of the comparison are as illustrated in FIGS. 3 to 5. FIG. 3shows the ECGs of Lead V7, FIG. 4 the ECGs of Lead V8, and FIG. 5 theECGs of Lead V9. It is confirmed from each drawing that the ECG(characteristic waveform A) based on the result of the arithmeticoperation is close to the ECG (characteristic waveform B) based on theactually measured values, and this assures extremely high precision.Incidentally, fifty four examples of ECGs were recorded for patients,healthy individuals, etc. in clinical practice, and the statisticsthereof demonstrated that the correlation coefficients between thewaveforms of the ECGs based on the arithmetic operation results and theECGs based on the actually measured values were approximately 0.83 (83%)on an average and that the tolerance ratio with the difference inpotential within 0.1 mV at the center point of the ST segment wasapproximately 73%. A close correlation with measurements is also shownsimilarly by the extended lead ECG waveforms as to Leads V_(3R), V_(4R),and V_(5R).

The method and apparatus for deriving the extended lead ECG in the firstembodiment, as described above, are able to easily derive through thearithmetic operation, the ECG signals of the extended lead ECG exceptfor the standard 12-lead ECG, from the ECG signals of the standard12-lead ECG measured by the potential detector. They are useful,particularly, in improvement in the diagnosis precision of themyocardial infarction for the heart muscle at the posterior wall, at theright lateral wall, or at the inferior wall. The deriving method asdescribed above is able to easily expand the functions of the ECGmonitors and Holter electrocardiographs and to achieve improvement inthe accuracy of diagnoses, for example, not only of the myocardialinfarction at the posterior wall, at the right lateral wall, or at theinferior wall, but also of the pulmonary heart, pulmonary embolus, rightventricular infarction, right ventricular hypertrophy, dextrocardia,other right ventricular stress-related diseases, and so on. It is alsofeasible to produce these electrocardiographs at low cost.

The first embodiment was described above, but it is noted that thederivation of the extended lead ECG in the present invention is notlimited to the derivation of the extended lead ECG of Leads V7, V8, andV9 at the electrode locations on the extensions of the chest leads andLeads V3R, V4R, V5R, and V6R at the electrode locations symmetric withthe electrode locations of the chest leads. The present invention isalso applicable to derivation of other extended lead ECGs. In addition,numerous design changes can be made without departing from the spirit ofthe invention.

Second Embodiment

The second embodiment will be described below. The second embodiment isdifferent from the first embodiment in that the extended lead ECG (LeadsV7, V8, V9, V_(3R), V_(4R), and V_(5R)) is derived by use of the leadvectors, instead of the transfer coefficients α.

(Principle of Method of Deriving Extended Lead ECG Using Lead Vectors)

The principle of the method of deriving the extended lead ECG accordingto the second embodiment is as described below. In the clinical ECG,according to the lead theory, the cardiac source at an arbitrary timecan be expressed by a Fixed Single Dipole, as described above, and apotential (V) at an arbitrary lead location can be determined by Eqs(2-1) to (2-3) below. $\begin{matrix}{V = {L \cdot H}} & \left( {2\text{-}1} \right) \\{H = \begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}} & \left( {2\text{-}2} \right) \\{L = \begin{pmatrix}{lx} \\{ly} \\{lz}\end{pmatrix}} & \left( {2\text{-}3} \right)\end{matrix}$

In the above equations, V represents the potential, H the heart vector,and L a lead vector.

When the measured lead potentials of the standard 12-lead ECG areapplied to Eq (2-1), Eq (2-4) below results. $\begin{matrix}{{\begin{pmatrix}L_{I}^{T} \\L_{II}^{T} \\L_{1}^{T} \\L_{2}^{T} \\L_{3}^{T} \\L_{4}^{T} \\L_{5}^{T} \\L_{6}^{T}\end{pmatrix}\begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}} = \begin{pmatrix}V_{I} \\V_{II} \\V_{1} \\V_{2} \\V_{3} \\V_{4} \\V_{5} \\V_{6}\end{pmatrix}} & \left( {2\text{-}4} \right)\end{matrix}$

In the above equation, T represents the transposition of a vector.

Eq (2-4) reduces to general formula L·H=V, and the heart vector H isderived from this Eq (2-4), obtaining Eq (2-5) below.H=(L ^(T) L)⁻¹ L ^(T) V  (2-5)

Based on Eq (2-5) above, the potentials V of the extended leads can bedetermined by Eq (2-6) below. $\begin{matrix}{\begin{pmatrix}V_{7} \\V_{8} \\V_{9} \\V_{3\quad R} \\V_{4R} \\V_{5\quad R}\end{pmatrix} = {\begin{pmatrix}L_{7}^{T} \\L_{8}^{T} \\L_{9}^{T} \\L_{3\quad R}^{T} \\L_{4\quad R}^{T} \\L_{5\quad R}^{T}\end{pmatrix}\begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}}} & \left( {2\text{-}6} \right)\end{matrix}$(Configuration of Electrocardiograph with Function for Deriving ExtendedLead ECG)

FIG. 6 is a system configuration diagram of an electrocardiograph forderiving the ECG signals of the extended lead ECG from the ECG signalsof the standard 12-lead ECG in the second embodiment. Theelectrocardiograph in the second embodiment is different in thearithmetic processing of the extended lead ECG in extended lead ECGcalculator 17 from the electrocardiograph in the first embodiment.Specifically, the extended lead ECG calculator 17 receives the ECGsignals (I, II, V1, V2, V3, V4, V5, and V6) from the ECG signal memory12 and then retrieves the lead vectors of I, II, V1, V2, V3, V4, V5, andV6 being the measured leads stored in lead vector storage 13, anddetermines the heart vector H on the basis of Eq (2-4) and Eq (2-5).Furthermore, the extended lead ECG calculator 17 retrieves the leadvectors L of the extended leads from the lead vector storage 13 andcalculates the extended lead ECG (V7, V8, V9, V_(3R), V_(4R), andV_(5R)), based on Eq (2-6).

The operation of the electrocardiograph shown in FIG. 6 will bedescribed below with reference to the flowchart of theelectrocardiograph shown in FIG. 7. First, the potential detector 10measures the ECG signals (I, II, V1, V2, V3, V4, V5, and V6) of thestandard 12-lead ECG of a patient (STEP-201). The ECG signals of thestandard 12-lead ECG thus measured are stored into the ECG signal memory12 (STEP-202). Then the ECG signals (I, II, V1, V2, V3, V4, V5, and V6)stored in the ECG signal memory 12 are fed to the extended lead ECGcalculator 17. The extended lead ECG calculator 17 retrieves the leadvectors of I, II, V1, V2, V3, V4, V5, and V6 of the measured leads fromthe lead vector storage 13 (STEP-203). Then the extended lead ECGcalculator 17 determines the heart vector H on the basis of Eq (2-4) andEq (2-5), using the lead vectors of I, II, V1, V2, V3, V4, V5, and V6(STEP-204). Furthermore, the lead vectors of the extended leads (L₇^(T), L₈ ^(T), L₉ ^(T), L_(3R) ^(T), L_(4R) ^(T), and L_(5R) ^(T)) arefed from the lead vector storage 13 into the extended lead ECGcalculator 17 (STEP-205). Thereafter, the extended lead ECG calculator17 calculates the extended lead ECG (V7, V8, V9, V_(3R), V_(4R), andV_(5R)) from the heart vector H and the lead vectors of the extendedleads, based on Eq (2-6) (STEP-206).

The ECG signals (V7, V8, V9, V_(3R), V_(4R), and V_(5R)) of the extendedlead ECG calculated in this manner are outputted to the extended leadECG waveform output device 18 and subjected to waveform processing bythe extended lead ECG waveform output device 18, and the result is fedto the display monitor 20 (STEP-207). The ECG signals (I, II, V1, V2,V3, V4, V5, and V6) of the standard 12-lead ECG stored in the ECG signalmemory 12 are also outputted to the standard 12-lead ECG waveform outputdevice 14 and subjected to waveform processing by this standard 12-leadECG waveform output device 14, and the result is fed to the displaymonitor 20 (STEP-208). The display monitor 20 simultaneously displays ona display screen, the standard 12-lead ECG and the extended lead ECGthus fed (STEP-209).

The method and apparatus for deriving the extended lead ECG in thesecond embodiment, as described above, are able to easily derive throughthe arithmetic operation, the ECG signals of the extended lead ECGexcept for the standard 12-lead ECG, from the ECG signals of thestandard 12-lead ECG measured by the potential detector, as in the firstembodiment. They are useful, particularly, in improvement in thediagnosis precision of the myocardial infarction for the heart muscle atthe posterior wall, at the right lateral wall, or at the inferior wall.The deriving method as described above is able to easily expand thefunctions of the ECG monitors and Holter electrocardiographs and toachieve improvement in the accuracy of diagnoses, for example, not onlyof the myocardial infarction at the posterior wall, at the right lateralwall, or at the inferior wall, but also of the pulmonary heart,pulmonary embolus, right ventricular infarction, right ventricularhypertrophy, dextrocardia, other right ventricular stress-relateddiseases, and so on. It is also feasible to produce theseelectrocardiographs at low cost.

Third Embodiment

In view of the invention in Patent Document 1 by the Inventor, Leads Iand II of the limb leads and the two leads of Leads V2 and V4 of thechest leads in the standard 12-lead ECG are used as the subset of thelead system consisting of the minimum number of channels, for example,with the potential detector consisting of six electrodes to determine(1) Lead III and Leads aV (Lead aVR, Lead aVL, and Lead aVF) by thearithmetic operation based on the characteristic relationship among theleads presented in [Table 1] above. In addition, (2) the rest leads ofthe chest leads, Leads V1, V3, V5, and V6, are determined by thearithmetic operation based on the relationship among the potentials [V],lead vectors [L], and heart vector [H].

In the third embodiment, therefore, the extended lead potentials (ECGsignals of V7, V8, V9 and V_(3R), V_(4R), V_(5R)) of the extended leadECG except for the standard 12-lead ECG are calculated by an arithmeticoperation from the standard lead potentials (ECG signals of I, II, V2,and V4) of the standard 12-lead ECG measured by the potential detectorconsisting of ten or less electrodes.

In this case, in order to detect the ECG signals of Leads I and II amongthe standard lead potentials of the standard 12-lead ECG, the electrodesare mounted at four locations, the left and right arms (electrodes LA,RA) and the left and right lower limbs (electrodes LL, RL), for the limbleads. In the case of an exercise stress test or the like, theelectrodes are mounted at four locations, the distal sites of the leftand right clavicles as left and right upper limbs and the left and rightsides of the abdomen as left and right lower limbs, to measure the limbleads among the Mason-Likar modified 12 leads as a modification of thestandard 12 leads. The electrode RL serves as a ground electrode.Furthermore, in order to measure the ECG signals of two leads (V2, V4)of the chest leads among the standard lead potentials, the electrodesare mounted at two locations: e.g., the fourth rib intercostal space atthe left margin of sternum (to obtain the ECG signal of V2) and anintersection between the midline of the left clavicle and a horizontalline traversing the fifth intercostal space (to obtain the ECG signal ofV4). In this manner, using the subset (part) of the lead system of thestandard 12-lead ECG, the other lead potentials (ECG signals) of thestandard 12-lead ECG can be determined based on the characteristicrelationship among the leads presented in [Table 1] above or based onthe relationship among the potential vector, the lead vector, and theheart vector. The measurement with the subset of modified 12 leads alsoallows us to obtain the modified 12-lead ECG and extended lead ECGthereof in the same manner. An embodiment of the deriving method of theextended lead ECG and the electrocardiograph with the extended leadfunction will be specifically described below.

(Principle of Method of Deriving Extended Lead ECG from Lead Vectors)

The principle of the deriving method of the extended lead ECG accordingto the third embodiment is as described below. In the clinical ECG, asdescribed previously, the cardiac source at an arbitrary time can beexpressed by a Fixed Single Dipole according to the lead theory and apotential (V) at an arbitrary lead location can be determined by Eqs(3-1) to (3-3) below. $\begin{matrix}{V = {L \cdot H}} & \left( {3\text{-}1} \right) \\{H = \begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}} & \left( {3\text{-}2} \right) \\{L = \begin{pmatrix}{lx} \\{ly} \\{lz}\end{pmatrix}} & \left( {3\text{-}3} \right)\end{matrix}$

In the above equations, V represents a potential, H the heart vector,and L a lead vector.

Since the heart vector H is a spatial vector fixed in position, it hasonly three independent parameters. Therefore, the parameters of theheart vector H can be determined from three leads having spatialinformation. It follows that once the heart vector H is determined, thepotentials of the remaining leads of the 12 leads can also be determinedby calculation.

For example, the lead potentials of the extended leads (V7, V8, V9,V_(3R), V_(4R), and V_(5R)) can be derived by an arithmetic operation asexpressed by Eq (3-4) below, based on the measurement of ECG signals ofthe lead locations (I, II, V2, and V4) as standard lead potentials ofthe standard 12-lead ECG. $\begin{matrix}{{\begin{pmatrix}L_{I}^{T} \\L_{II}^{T} \\L_{2}^{T} \\L_{4}^{T}\end{pmatrix}\begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}} = \begin{pmatrix}V_{I} \\V_{II} \\V_{2} \\V_{4}\end{pmatrix}} & \left( {3\text{-}4} \right)\end{matrix}$

In this equation, T represents the transposition of a vector.

Eq (3-4) reduces to the general formula L·H=V. Therefore, the heartvector H is determined from this Eq (3-4) to obtain Eq (3-5) below.H=(L ^(T) L)⁻¹ L ^(T) V  (3-5)

The potentials V of the extended leads can be determined by Eq (3-6)below, based on above Eq (3-5). $\begin{matrix}{\begin{pmatrix}V_{7} \\V_{8} \\V_{9} \\V_{3\quad R} \\V_{4\quad R} \\V_{5\quad R}\end{pmatrix} = {\begin{pmatrix}L_{7}^{T} \\L_{8}^{T} \\L_{9}^{T} \\L_{3\quad R}^{T} \\L_{4\quad R}^{T} \\L_{5\quad R}^{T}\end{pmatrix}\begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}}} & \left( {3\text{-}6} \right)\end{matrix}$[Configuration of Electrocardiograph with Function for Deriving ExtendedLead ECG]

FIG. 8 is a system configuration diagram of an electrocardiograph with afunction of deriving an extended lead ECG in the third embodiment. InFIG. 8, specifically, reference symbol 10A denotes a potential detectorfor measuring the ECG signals as standard lead potentials of thestandard 12-lead ECG. This potential detector 10A functions as abioamplifier and as an A/D converter for measuring the ECG signals (I,II, V2, and V4) from ten or less electrodes mounted on a body surface ofa living body for obtaining the standard lead potentials of the standard12-lead ECG; i.e., the subset of the potential detector for the standard12-lead ECG (e.g., the six electrodes of RA, LA, RL, LL, V2, and V4).

The ECG signals (I, II, V2, and V4) of the standard 12-lead potentialsdetected by this potential detector 10A are stored each into the ECGsignal memory 12A and fed to a standard 12-lead ECG calculator 14A. TheECG signals (I, II, V2, and V4) stored in this ECG signal memory 12A arealso fed to an extended lead ECG calculator 17A. Then the extended leadECG calculator 17A retrieves the lead vectors of I, II, V2, and V4 beingthe measured leads stored in a lead vector storage 13A, and determinesthe heart vector [H] on the basis of Eq (3-4) and Eq (3-5). Furthermore,the extended lead ECG calculator 17A retrieves the extended lead vectors[L] (L₇ ^(T), L₈ ^(T), L₉ ^(T), L_(3R) ^(T), L_(4R) ^(T), and L_(5R)^(T)) from the lead vector storage 13A and performs an arithmeticoperation to calculate the ECG signals (V7, V8, V9, V_(3R), V_(4R), andV_(5R)) as extended lead potentials of the extended lead ECG on thebasis of Eq (3-6).

The ECG signals as extended lead potentials calculated in this manner bythe extended lead ECG calculator 17A are fed to an extended lead ECGwaveform output device 18A. The standard 12-lead potentials calculatedby the standard 12-lead ECG calculator 14A are fed to a standard 12-leadECG waveform output device 20A.

Then the ECG waveform outputs from the standard 12-lead ECG waveformoutput device 20A and from the extended lead ECG waveform output device18A are fed each to a display monitor 22A and are arranged tosimultaneously display images of the standard 12-lead ECG and theextended lead ECG.

The system operation of the electrocardiograph with the extended leadfunction constructed as described above will be described below withreference to the flowchart shown in FIG. 9.

First, in the electrocardiograph with the extended lead function, thepotential detector 10A measures the ECG signals (I, II, V2, and V4) asstandard lead potentials of the standard 12-lead ECG of a patient(STEP-301). The ECG signals (I, II, V2, and V4) of the standard leadpotentials thus measured are stored into the ECG signal memory 12A(STEP-302).

The extended lead ECG calculator 17A retrieves the lead vectors of I,II, V2, and V4 as the measured leads from the lead vector storage 13A(STEP-303). Furthermore, the extended lead ECG calculator 17A uses theselead vectors of I, II, V2, and V4 to perform an arithmetic operation tocalculate the heart vector [H] from Eq (3-4) and Eq (3-5) representingthe relationships among the potentials [V], lead vectors [L], and heartvector [H] concerning the leads, based on the ECG signals (I, II, V2,and V4) of the patient stored in the ECG signal memory 12A (STEP-304).The lead vectors (L₇ ^(T), L₈ ^(T), L₉ ^(T), L_(3R) ^(T), L_(4R) ^(T),and L_(5R) ^(T)) of the extended leads are fed from the lead vectorstorage 13A to the extended lead ECG calculator 17A (STEP-305).Thereafter, the extended lead ECG calculator 17A performs an arithmeticoperation to calculate the ECG signals (V7, V8, V9, V_(3R), V_(4R), andV_(5R)) of the extended lead ECG from the heart vector [H] and the leadvectors of the extended leads, based on Eq (3-6) (STEP-306).

On the other hand, the ECG signals (I, II, V2, and V4) stored in the ECGsignal memory 12A are fed to the standard 12-lead ECG calculator 14A,which performs the arithmetic operation to calculate the lead potentials(I, II, III, V1, V2, V3, V4, V5, V6, aVR, aVL, aVF) of the standard12-lead ECG. Here Leads V1, V3, V5, and V6 are calculated based on therelationship among the potential vector, lead vectors, and heart vector,using the heart vector [H] determined at STEP-304, and the lead vectors(L₁ ^(T), L₃ ^(T), L₅ ^(T), L₆ ^(T)). The lead potentials of thestandard 12-lead ECG calculated by the standard 12-lead ECG calculator14A are subjected to waveform processing by the standard 12-lead ECGwaveform output device 20A and the result is fed to the display monitor22A (STEP-307).

Then the ECG signals (V7, V8, V9, V_(3R), V_(4R), and V_(5R)) asextended lead potentials of the extended lead ECG calculated by theextended lead ECG calculator 17A are subjected to waveform processing bythe extended lead ECG waveform output device 18A and the result is fedto the display monitor 22A (STEP-308). Furthermore, the extended leadECG waveform output and the standard 12-lead ECG waveform outputresulting from the waveform processing are simultaneously displayed on adisplay screen of the display monitor 22A (STEP-309).

Fourth Embodiment

[Method of Deriving Extended Lead ECG Making Use of Relationship AmongLeads (Transfer Coefficients α)]

The lead theory based on the dipole model of the heart is a theory mostused in clinical application nowadays. A potential (V) at an arbitrarylead location can be determined by Eqs (4-1) to (4-3) below.$\begin{matrix}{V = {L \cdot H}} & \left( {4\text{-}1} \right) \\{H = \begin{pmatrix}{hx} \\{hy} \\{hz}\end{pmatrix}} & \left( {4\text{-}2} \right) \\{L = \begin{pmatrix}{lx} \\{ly} \\{lz}\end{pmatrix}} & \left( {4\text{-}3} \right)\end{matrix}$

In the above equations, V represents a potential matrix, H the heartvector, and L a lead vector.

According to this lead theory, as described above, a heart potential atan arbitrary lead location is determined by three parameters. Therefore,ECG potentials at three or more arbitrary locations on a body surfacehave a correlation to each other. Specifically, some lead potentials canbe expressed by linear combination of the other lead potentials. Forexample, there is the relationship represented by Eq (4-4) below.$\begin{matrix}{V_{i} = {\sum\limits_{j}{\alpha_{i,j}V_{j}}}} & \left( {4\text{-}4} \right)\end{matrix}$

[In the above relationship, i represents a lead number of each extendedlead location (V7, V8, V9, V_(3R), V_(4R), or V_(5R)), and j a leadnumber of each standard lead potential of the standard 12 leads (I, II,V2, and V4). α stands for transfer coefficients representing therelationship among the leads.] Theoretically, the transfer coefficientsα are constants determined by the torso structure of each individual andare unknowns in above Eq (4-4). On the contrary, however, it is alsopossible to actually measure the lead potentials at the respective leadlocations (V7, V8, V9, V_(3R), V_(4R), V_(5R) and I, II, V2, V4) inadvance and to determine the transfer coefficients α, as in Eq (4-5)below, from the above Eq (4-4).A=(V ^(T) _(j) V _(j))⁻¹ V ^(T) _(j) V _(i)  (4-5)

In the above relation, A={α_(ij)}

V_(j)={V_(s,j)}

V_(i)={V_(i,s)}

i represents a lead number of each extended lead location (V7, V8, V9,V_(3R), V_(4R), or V_(5R)), j a lead number of each standard leadpotential of the standard 12 leads (I, II, V2, and V4), and s a datasample.

Once the transfer coefficients α are determined in this manner, theextended lead potentials (V7, V8, V9, V_(3R), V_(4R), and V_(5R)) of theextended lead ECG can be instantly determined from the ECG signals (I,II, V2, and V4) as standard lead potentials of the standard 12-lead ECG,according to Eq (4-5) above.

In the present embodiment, an ideal way for calculation of the extendedleads of a specific person is to determine the transfer coefficients αof the specific individual in advance, store them as data, and use themfor the arithmetic operation, which can yield the arithmetic operationresult with high accuracy. It is, however, not practical in some casesto first determine the transfer coefficients α of the individual, storethem as data, and keep them available for the arithmetic operation asneeded. In such cases, therefore, the transfer coefficients α of anaverage human model are determined and are stored as data to be readyfor use in the arithmetic operation as needed. For this purpose, forexample, ECGs are measured from many people, for example, on theoccasion of group medical examination, to collect the ECG signalsconsisting of the two leads I and II of the limb leads and the two leadsV2 and V4 of the chest leads out of the standard 12 leads and theextended lead potentials V7, V8, V9, V_(3R), V_(4R), and V_(5R), andthereby construct a database for calculation of the transfercoefficients α for the arithmetic operation. Then the entire data of thegroup stored in this database is applied to aforementioned Eq (4-5) todetermine average α values and the α values thus obtained are storedinto a predetermined memory for feeding them to a calculator forcalculating the extended lead potentials.

In the embodiments described above, the derivation of the extended leadECG was described using Leads V7, V8, V9 at the electrode locations onextensions of the chest leads and Leads V3R, V4R, and V5R at theelectrode potentials symmetric with the electrode locations of the chestleads, but, without having to be limited to these, the present inventioncan also be applied to derivation of other extended lead ECGs. In theembodiments described above, the extended lead ECG was calculated fromLeads I, II, V2, and V4 being the standard lead potentials, but, withouthaving to be limited to this, the extended lead ECG can also becalculated by using various combinations of other two limb leads and twochest leads of the standard 12 leads. Particularly, combinations ofpractical use include a combination of Leads I, II, V2, and V5, acombination of Leads I, II, V2, and V6, a combination of Leads I, II,V1, and V4, a combination of Leads I, II, V1, and V5, and a combinationof Leads I, II, V1, and V6.

Described below is an electrocardiograph with the extended lead functionarranged to be able to simultaneously display the extended lead ECG andthe standard 12-lead ECG on a screen of a display monitor, based on thederivation method of the extended lead ECG described in the fourthembodiment.

[Configuration of Electrocardiograph with Function for Derivation ofExtended Lead ECG]

FIG. 10 is a system configuration diagram of an electrocardiograph witha function of deriving the extended lead ECG in the fourth embodiment.In FIG. 10, specifically, reference symbol 10A denotes a potentialdetector for measuring the ECG signals as standard lead potentials ofthe standard 12-lead ECG. This potential detector 10A functions as abioamplifier and as an A/D converter for measuring the ECG signals (I,II, V2, and V4) from ten or less electrodes mounted on a body surface ofa living body for acquisition of the standard lead potentials of thestandard 12-lead ECG, i.e., a subset (e.g., the six electrodes of RA,LA, RL, LL, V2, and V4) of the potential detector for the standard12-lead ECG.

The ECG signals (I, II, V2, and V4) of the standard 12-lead potentialsdetected by this potential detector 10A are stored each into the ECGsignal memory 12A and fed to the standard 12-lead ECG calculator 14A.The ECG signals (I, II, V2, and V4) stored in this ECG signal memory 12Aare fed to the extended lead ECG calculator 16A, which performs thearithmetic operation to calculate the ECG signals (V7, V8, V9, V_(3R),V_(4R), and V_(5R)) as extended lead potentials of the extended leadECG.

As described later in detail, the ECG signals (V7, V8, V9, V_(3R),V_(4R), and V_(5R)) are calculated according to above Eq (4-1), based onthe ECG signals (I, II, V2, and V4) as the standard lead potentials ofthe standard 12-lead ECG measured, using the transfer coefficients α forthe arithmetic operation set in advance in the memory 15A.

The ECG signals as the extended lead potentials calculated in thismanner by the extended lead ECG calculator 16A are fed to the extendedlead ECG waveform output device 18A. Furthermore, the ECG signals as thestandard 12-lead potentials calculated by the standard 12-lead ECGcalculator 14A are fed to the standard 12-lead ECG waveform outputdevice 20A.

Then the ECG waveform outputs from the standard 12-lead ECG waveformoutput device 20A and from the extended lead ECG waveform output device18A are fed each to the display monitor 22A to display images of thestandard 12-lead ECG and the extended lead ECG simultaneously.

For that, the extended lead ECG calculator 16A collects the ECG signalsconsisting of two Leads I, II of the limb leads and two Leads V2, V4 ofthe chest leads out of the standard 12 leads, and the extended leadpotentials V7, V8, V9, V_(3R), V_(4R), and V_(5R) recorded from a numberof patients, healthy individuals, etc. by the potential detector 10A,constructs a database for calculation of the calculation transfercoefficients α of an average model, and stores the calculation transfercoefficients α calculated using the database, into the memory 15A. Inthis case, the calculation transfer coefficients α can be calculatedaccording to Eq (4-5).

The system operation of the electrocardiograph with the extended leadfunction constructed in this manner will be described below withreference to the flowchart shown in FIG. 11.

In the electrocardiograph with the extended lead function, first, thepotential detector 10A measures the ECG signals (I, II, V2, and V4) asthe standard lead potentials of the standard 12-lead ECG of a patient(STEP-401). The ECG signals (I, II, V2, and V4) of the standard leadpotentials thus measured are stored into the ECG signal memory 12A(STEP-402).

Next, the calculation transfer coefficients α preliminarily set in thememory 15A are fed to the extended lead ECG calculator 16A (STEP-403),and the ECG signals (I, II, V2, and V4) stored in the ECG signal memory12A are also fed to the extended lead ECG calculator 16A, whereupon theextended lead ECG calculator 16A calculates the ECG signals (V7, V8, V9,V_(3R), V_(4R), and V_(5R)) of the extended lead ECG, based on the ECGsignals (I, II, V2, and V4) and the transfer coefficients α (STEP-404).The arithmetic operation to calculate the ECG signals (V7, V8, V9,V_(3R), V_(4R), and V_(5R)) of the extended lead ECG by the extendedlead ECG calculator 16A can be performed as follows, based on Eq (4-4).Lead V7: V ₇=α_(7I) V _(I)+α_(7II) V _(II)+α_(7V2) V _(V2)+α_(7V4) V_(V4)  (4-6)Lead V8: V8=α_(8I) V _(I)+α_(8II) V _(II)+α_(8V2) V _(V2)+α_(8V4) V_(V4)  (4-7)Lead V9: V ₉=α_(9I) V _(I)+α_(9II) V _(II)+α_(9V2) V _(V2)+α_(9V4) V_(V4)  (4-8)Lead V _(3R) : V _(3R)=α_(3RI) V _(I)+α_(3RII) V _(II)+α_(3RV2) V_(V2)+α_(3RV4) V _(V4)  (4-9)Lead V _(4R) : V _(4R)=α_(4RI) V _(I)+α_(4RII) V _(II)+α_(4RV2) V_(V2)+α_(4RV4) V _(V4)  (4-10)Lead V _(5R) : V _(5R)=α_(5RI) V _(I)+α_(5RII) V _(II)+α_(5RV2) V_(V2)+α_(5RV4) V _(V4)  (4-11)

The ECG signals (I, II, V2, and V4) of the standard lead potentialsstored in the ECG signal memory 12A are also fed to the standard 12-leadECG calculator 14A, which performs the arithmetic operation to calculatethe lead potentials (I, II, III, V1, V2, V3, V4, V5, V6, aVR, aVL, andaVF) of the standard 12-lead ECG (STEP-405). Here the lead potentialsV1, V3, V5, and V6 are determined by the arithmetic operation based onthe relationship among the potential vector, lead vector, and heartvector.

The ECG signals (V7, V8, V9, V_(3R), V_(4R), and V_(5R)) as the extendedlead potentials of the extended lead ECG calculated by the extended leadECG calculator 16A are subjected to waveform processing by the extendedlead ECG waveform output device 18A and the result is fed to the displaymonitor 22A (STEP-406). The ECG signals (I, II, III, V1, V2, V3, V4, V5,V6, aVR, aVL, and aVF) as the lead potentials of the standard 12-leadECG calculated by the standard 12-lead ECG calculator 14A are subjectedto waveform processing by the standard 12-lead ECG waveform outputdevice 20A (STEP-407) and the result is fed to the display monitor 22A(STEP-407). Furthermore, the extended lead ECG waveform output and thestandard 12-lead ECG waveform output resulting from the waveformprocessing are simultaneously displayed on the display screen of thedisplay monitor 22A (STEP-408).

FIGS. 12 to 18 show the waveform diagrams of the ECG signals (I, II,V1-V6) as the measured standard lead potentials of the standard 12leads, and Leads V7, V8, V9 and Leads V3R, V4R, V5R as extended leadECGs on the basis of the fourth embodiment. Similar output waveforms arealso obtained by the third embodiment.

Specifically, FIG. 12(a) shows the waveforms of the ECG signals (I, II,V2, and V4) measured from a certain patient. FIG. 12(b) shows thewaveforms of the respective leads V3R, V4R, and V5R as the extended leadECG calculated from the ECG signals (I, II, V2, and V4), and thewaveforms of the respective leads V3R, V4R, and V5R actually measuredfrom the same patient (wherein the measured waveforms are indicated bythick solid lines and wherein portions overlapping with the waveformscalculated by the arithmetic operation are indicated by thin solidlines). FIG. 12(c) shows the waveforms of Leads V7, V8, and V9 (asindicated by thin solid lines) as the extended lead ECG calculated fromthe ECG signals (I, II, V2, and V4), and the waveforms of the respectiveleads V7, V8, and V9 actually measured from the same patient (whereinthe measured waveforms are indicated by thick solid lines and whereinportions overlapping with the waveforms calculated by the arithmeticoperation are indicated by thin solid lines). This result confirms thatthe waveforms of the extended lead ECG obtained by the calculation basedon the fourth embodiment are extremely close to those of the extendedlead ECG obtained by actual measurement.

FIG. 13(a) shows the waveforms of the ECG signals (I, II, V2, and V5)measured from another patient. FIG. 13(b) shows the waveforms of therespective leads V3R, V4R, and V5R as the extended lead ECG calculatedfrom the ECG signals (I, II, V2, and V5), and the waveforms of therespective leads V3R, V4R, and V5R actually measured from the samepatient (wherein the measured waveforms are indicated by thick solidlines and wherein portions overlapping with the waveforms calculated bythe arithmetic operation are indicated by thin solid lines). FIG. 13(c)shows the waveforms of the respective leads V7, V8, and V9 (as indicatedby thin solid lines) as the extended lead ECG calculated from the ECGsignals (I, II, V2, and V5), and the waveforms of the respective leadsV7, V8, and V9 actually measured from the same patient (wherein themeasured waveforms are indicated by thick solid lines and whereinportions overlapping with the waveforms calculated by the arithmeticoperation are indicated by thin solid lines). This result confirms thatthe waveforms of the extended lead ECG obtained by calculation based onthe fourth embodiment are extremely close to the waveforms of theextended lead ECG obtained by actual measurement.

FIG. 14(a) shows the waveforms of the ECG signals (I, II, V2, and V6)measured from another patient. FIG. 14(b) shows the waveforms of therespective leads V3R, V4R, and V5R as the extended lead ECG calculatedfrom the ECG signals (I, II, V2, and V6), and the waveforms of therespective leads V3R, V4R, and V5R actually measured from the samepatient (wherein the measured waveforms are indicated by thick solidlines and wherein portions overlapping with the waveforms calculated bythe arithmetic operation are indicated by thin solid lines). FIG. 14(c)shows the waveforms of the respective leads V7, V8, and V9 (as indicatedby thin solid lines) as the extended lead ECG calculated from the ECGsignals (I, II, V2, and V6), and the waveforms of the respective leadsV7, V8, and V9 actually measured from the same patient (wherein themeasured waveforms are indicated by thick solid lines and whereinportions overlapping with the waveforms calculated by the arithmeticoperation are indicated by thin solid lines). This result confirms thatthe waveforms of the extended lead ECG obtained by calculation based onthe fourth embodiment are extremely close to the waveforms of theextended lead ECG obtained by actual measurement.

FIG. 15(a) shows the waveforms of the ECG signals (I, II, V1, and V5)measured from another patient. FIG. 15(b) shows the waveforms of therespective leads V3R, V4R, and V5R as the extended lead ECG calculatedfrom the ECG signals (I, II, V1, and V5), and the waveforms of therespective leads V3R, V4R, and V5R actually measured from the samepatient (wherein the measured waveforms are indicated by thick solidlines and wherein portions overlapping with the waveforms calculated bythe arithmetic operation are indicated by thin solid lines). FIG. 15(c)shows the waveforms of the respective leads V7, V8, and V9 (as indicatedby thin solid lines) as the extended lead ECG calculated from the ECGsignals (I, II, V1, and V5), and the waveforms of the respective leadsV7, V8, and V9 actually measured from the same patient (wherein themeasured waveforms are indicated by thick solid lines and whereinportions overlapping with the waveforms calculated by the arithmeticoperation are indicated by thin solid lines). This result confirms thatthe waveforms of the extended lead ECG obtained by calculation based onthe fourth embodiment are extremely close to the waveforms of theextended lead ECG obtained by actual measurement.

FIG. 16(a) shows the waveforms of the ECG signals (I, II, V1, and V6)measured from another patient. FIG. 16(b) shows the waveforms of therespective leads V3R, V4R, and V5R as the extended lead ECG calculatedfrom the ECG signals (I, II, V1, and V6), and the waveforms of therespective leads V3R, V4R, and V5R actually measured from the samepatient (wherein the measured waveforms are indicated by thick solidlines and wherein portions overlapping with the waveforms calculated bythe arithmetic operation are indicated by thin solid lines). FIG. 16(c)shows the waveforms of the respective leads V7, V8, and V9 (as indicatedby thin solid lines) as the extended lead ECG calculated from the ECGsignals (I, II, V1, and V6), and the waveforms of the respective leadsV7, V8, and V9 actually measured from the same patient (wherein themeasured waveforms are indicated by thick solid lines and whereinportions overlapping with the waveforms calculated by the arithmeticoperation are indicated by thin solid lines). This result confirms thatthe waveforms of the extended lead ECG obtained by calculation based onthe fourth embodiment are extremely close to the waveforms of theextended lead ECG obtained by actual measurement.

FIG. 17(a) shows the waveforms of the ECG signals (I, II, V3, and V4)measured from another patient. FIG. 17(b) shows the waveforms of therespective leads V3R, V4R, and V5R as the extended lead ECG calculatedfrom the ECG signals (I, II, V3, and V4), and the waveforms of therespective leads V3R, V4R, and V5R actually measured from the samepatient (wherein the measured waveforms are indicated by thick solidlines and wherein portions overlapping with the waveforms calculated bythe arithmetic operation are indicated by thin solid lines). FIG. 17(c)shows the waveforms of the respective leads V7, V8, and V9 (as indicatedby thin solid lines) as the extended lead ECG calculated from the ECGsignals (I, II, V3, and V4), and the waveforms of the respective leadsV7, V8, and V9 actually measured from the same patient (wherein themeasured waveforms are indicated by thick solid lines and whereinportions overlapping with the waveforms calculated by the arithmeticoperation are indicated by thin solid lines). This result confirms thatthe waveforms of the extended lead ECG obtained by calculation based onthe fourth embodiment are extremely close to the waveforms of theextended lead ECG obtained by actual measurement.

FIG. 18(a) shows the waveforms of the ECG signals (I, II, V3, and V5)measured from another patient. FIG. 18(b) shows the waveforms of therespective leads V3R, V4R, and V5R as the extended lead ECG calculatedfrom the ECG signals (I, II, V3, and V5), and the waveforms of therespective leads V3R, V4R, and V5R actually measured from the samepatient (wherein the measured waveforms are indicated by thick solidlines and wherein portions overlapping with the waveforms calculated bythe arithmetic operation are indicated by thin solid lines). FIG. 18(c)shows the waveforms of the respective leads V7, V8, and V9 (as indicatedby thin solid lines) as the extended lead ECG calculated from the ECGsignals (I, II, V3, and V5), and the waveforms of the respective leadsV7, V8, and V9 actually measured from the same patient (wherein themeasured waveforms are indicated by thick solid lines and whereinportions overlapping with the waveforms calculated by the arithmeticoperation are indicated by thin solid lines). This result confirms thatthe waveforms of the extended lead ECG obtained by calculation based onthe fourth embodiment are extremely close to the waveforms of theextended lead ECG obtained by actual measurement.

It is noted that the present invention is by no means limited to theabove embodiments. In the above embodiments, Leads I and II of the limbleads were selected and measured and the two leads of the chest leadswere selected and measured out of the standard lead potentials of thestandard 12-lead ECG (including the modified 12-lead ECG), and theextended lead ECG was determined from these leads. However, the presentinvention is not limited to such selection of leads, but the electrodesmay be optionally selected; concerning the limb leads, it is alsopossible to select a combination of Leads I and III or a combination ofLeads II and III. In this case, concerning the chest leads, it ispossible to select an arbitrary combination from Leads V1-V6, of course.The present invention also allows the use of the chest leads among theMason-Likar modified 12 leads to obtain the extended lead ECG of themodified 12-lead ECG in the case of an exercise load test or the like.The function of calculating the extended leads according to the presentinvention can also be added to the electrocardiographs in operation inhospital facilities and others, and can

1. An electrocardiograph with an extended lead function comprising: a potential detector for measuring at least certain lead potentials out of lead potentials of a 12-lead electrocardiogram (ECG); and extended lead potential calculating means for calculating an extended lead potential, based on the lead potentials of the 12-lead ECG measured by the potential detector.
 2. The electrocardiograph with the extended lead function according to claim 1, wherein the extended lead potential calculating means uses a relationship among the lead potentials, a heart vector, and lead vectors to determine the heart vector on the basis of the lead potentials measured by the potential detector, and calculates the extended lead potential by use of the heart vector thus determined.
 3. The electrocardiograph with the extended lead function according to claim 1, wherein the extended lead potential calculating means calculates the extended lead potential on the basis of the lead potentials measured by the potential detector, using transfer coefficients α representing a relationship among leads.
 4. The electrocardiograph with the extended lead function according to claim 3, wherein the transfer coefficients α are defined by the following equation: ${V_{i} = {\sum\limits_{j}{\alpha_{i,j}V_{j}}}},$ where i is a lead number of an extended lead and j a lead number of one of 12 leads.
 5. The electrocardiograph with the extended lead function according to any one of claims 1 to 4, wherein the potential detector measures at least two lead potentials out of limb leads and measures at least two lead potentials out of chest leads.
 6. The electrocardiograph with the extended lead function according to any one of claims 1 to 4, wherein the extended lead potential comprises at least one lead out of Leads V7-V9 and Leads V_(3R), V_(4R), V_(5R), and V_(6R).
 7. An extended lead ECG deriving method comprising: a first step of measuring at least certain lead potentials out of lead potentials of a 12-lead ECG; and a second step of calculating an extended lead potential, based on the lead potentials of the 12-lead ECG measured.
 8. The extended lead ECG deriving method according to claim 7, wherein the second step comprises using a relationship among the lead potentials, a heart vector, and lead vectors to determine the heart vector on the basis of the lead potentials measured, and calculating the extended lead potential by use of the heart vector thus determined.
 9. The extended lead ECG deriving method according to claim 7, wherein the second step comprises calculating the extended lead potential on the basis of the lead potentials measured, using transfer coefficients α representing a relationship among leads.
 10. The extended lead ECG deriving method according to claim 9, wherein the transfer coefficients α are defined by the following equation: ${V_{i} = {\sum\limits_{j}{\alpha_{i,j}V_{j}}}},$ where i is a lead number of an extended lead and j a lead number of one of 12 leads.
 11. The extended lead ECG deriving method according to any one of claims 7 to 10, wherein the first step comprises measuring at least two lead potentials out of limb leads and at least two lead potentials out of chest leads.
 12. The extended lead ECG deriving method according to any one of claims 7 to 10, wherein the extended lead potential comprises at least one lead out of Leads V7-V9 and Leads V_(3R), V_(4R), V_(5R), and V_(6R).
 13. A method of deriving an extended lead ECG, comprising performing an arithmetic operation to calculate a lead potential at an extended lead location except for a standard 12-lead ECG, based on ECG signals measured as standard lead potentials of the standard 12-lead ECG by a potential detector comprised of ten or less electrodes.
 14. A method of deriving an extended lead ECG, comprising, based on ECG signals measured as standard lead potentials of a standard 12-lead ECG by a potential detector comprised of ten or less electrodes, using a relationship among potentials [V], lead vectors [L], and a heart vector [H] to determine the heart vector [H] on the basis of the ECG signals as the standard lead potentials of the standard 12-lead ECG measured, and performing an arithmetic operation to calculate an extended lead potential of the extended lead ECG, using the heart vector [H] thus determined.
 15. A method of deriving an extended lead ECG, comprising storing ECG signals measured as standard lead potentials of a standard 12-lead ECG by a potential detector comprised of ten or less electrodes, performing an arithmetic operation to set transfer coefficients α for calculation of an extended lead potential on the basis of the standard lead potentials of the standard 12-lead ECG and extended lead potentials of the extended lead ECG measured in advance, and performing an arithmetic operation to calculate the extended lead potential of the extended lead ECG from the ECG signals measured as the standard lead potentials of the standard 12-lead ECG, using the transfer coefficients α set by the arithmetic operation.
 16. A method of deriving an extended lead ECG, comprising storing ECG signals measured as a standard 12-lead ECG by a potential detector, performing an arithmetic operation to set parameters for calculation of an extended lead ECG on the basis of lead potentials of the standard 12-lead ECG and lead potentials of the extended lead ECG measured in advance, and performing an arithmetic operation to calculate a lead potential of the extended lead ECG from the ECG signals measured as the standard 12-lead ECG, using the parameters set by the arithmetic operation.
 17. The method according to any one of claims 13 to 16, wherein the potential of the extended lead comprises at least one lead out of Leads V7-V9 and Leads V_(3R), V_(4R), V_(5R), and V_(6R).
 18. An electrocardiograph with an extended lead function comprising: electrodes to be mounted on a body surface of a living body in order to obtain lead waveforms of a standard 12-ECG; a potential detector for measuring ECG signals of the standard 12-lead ECG from the respective electrodes; an ECG signal memory for storing each of the ECG signals of the standard 12-lead ECG measured by the potential detector; standard 12-lead ECG waveform means for performing waveform processing of the standard 12-lead ECG with input of the ECG signals obtained via the ECG signal memory; extended lead ECG signal calculating means for calculating an ECG signal of an extended lead ECG on the basis of calculation parameters α preliminarily set by an arithmetic operation with input of the ECG signals obtained via the ECG signal memory; extended lead ECG waveform outputting means for performing waveform processing of the extended lead ECG with input of the ECG signal calculated by the extended lead ECG signal calculating means; and a display monitor for simultaneously displaying on a screen, the ECG waveform outputs from the standard 12-lead ECG waveform outputting means and from the extended lead ECG waveform outputting means.
 19. The electrocardiograph with the extended lead function according to claim 18, wherein the signal potential of the extended lead ECG comprises at least one lead out of Leads V7-V9 and Leads V_(3R), V_(4R), V_(5R), and V_(6R).
 20. The electrocardiograph with the extended lead function according to claim 5, wherein the extended lead potential comprises at least one lead out of Leads V7-V9 and Leads V_(3R), V_(4R), V_(5R), and V_(6R).
 21. The extended lead ECG deriving method according to claim 11, wherein the extended lead potential comprises at least one lead out of Leads V7-V9 and Leads V_(3R), V_(4R), V_(5R), and V_(6R). 